Stateside in America, there has recently been a damning report regarding the use of the well-known, ectoparasite product, the “Seresto” collar. Seresto collars are commonly used within the UK and may well be included in loyalty discounted pet healthcare schemes (including such as that used at my own practice).

The report claims that Seresto collars were linked to over 1700 pet deaths in the USA. And that, perhaps equally as worryingly, that the U.S EPA (Environmental Protection Agency) failed to alert the public of this. In this article, we probe a little closer into the product itself; its actions, uses and whether these claims hold any truth. Are these allegations appropriate and valid, or has the data been skewed? Do the claims truly relate to legitimate collars, or have unregulated counterfeit products created an unfair loss of consumer trust?

So, what is Seresto?

Marketed on as an “innovative form of flea and tick repellent” Seresto “applies two crucial active tick and flea repellents over the surface of your dog’s hair and skin”. Uniquely, Seresto collars provide 8 months of continual external parasite prevention. Formatted into a collar, the product is easy to use. And it is relatively hassle-free given there is no wetting of the fur such as that experienced with other topical parasite treatments. The extended length of activity appeals to owners, who in the UK, often use the collars from Easter time, through until the end of year, thereby covering the main tick “season” associated with warmer weathers.

And how does Seresto work?

Seresto dog collars contains two active ingredients, imidacloprid and flumethrin. These medications fight the common skin parasites fleas and ticks. Concentrated into the collar, the ingredients release continually, into the dog’s coat in a kind of “trickle feed” type manner, slowly, over many months.

The medications ensure the death of fleas at any point within their life cycle. Additionally, the animal’s immediate surroundings are protected against larval flea development for almost 3 months. The product may also be used for those dogs with flea allergic dermatitis (FAD) and associated skin signs.

For ticks, Seresto offers both repellent (anti-feeding) activity and efficacy against infestations. The product therefore forms part of an effective weapon against the prevention of tick-borne diseases, such as Ehrlichiosis and Babesiosis, which are commonplace in Europe. With the advent of warmer environmental conditions due to climate change and increased movement of dogs into (and back from) Europe, these diseases are also increasingly seen within the UK. As such, including a Seresto collar in your pets parasite regime, confers good and effective protection.

And the ingredients?

Imidacloprid is a common pesticide that has been used for many years in the pet pharmaceutical industry. It is considered a low-risk product and can also be found in products such as Advocate and Advantix. 

Flumethrin, a synthetic pyrethroid pesticide has also been both studied and used in companion animals for decades. 

So what are the claims?

As mentioned above, the claims are of “the popular flea collar” being linked to nearly 1700 pet deaths. Whilst the EPA continue to do nothing to inform the public of the risks. 

Vetster option 01 (Blog)

I think it is clear (and obvious!) to say, that none of us as Veterinarians ever want to do anything to affect your pet’s health in a detrimental fashion. Quite the opposite, of course. Our recommendations for treatments are based on the knowledge that medicines are only granted licences; once robust safety trials have been passed. We of course have enormous sympathy for anyone who believes that a medicine contributed to the ill-health of their beloved pet. 

However, unfortunately, in this reported article, those persons consulted regarding the safety of Seresto had neither speciality in veterinary toxicology nor parasitology. This is clearly a shame given those experts would have likely shone an informed and professional opinion upon the question of Seresto’s safety. The evidence was also somewhat anecdotal and perhaps the full picture was not clearly painted. 

And are the claims valid?

Hmm, possibly not… And for the various reasons mentioned below…

Seresto is a globally available product.

Prior to its registration and during its development, its safety data was carefully scrutinised by various regulatory bodies. In fact, by over 80 of these organisations. These included, at the time, the U.S EPA. All were happy that it passed the rigorous and demanding levels of safety required. As such, a product licence was authorised for its use.

Additionally, Seresto still currently remains on the market within the USA and in many other countries around the world. 

It also seems that interpretation of the information obtained may not be entirely accurate.

Tony Rumschlag, the manufacturer’s senior veterinary director was quoted as saying, “the recent media reports were based on raw data and cannot be used to draw conclusions on what may have actually caused the issues”.  It is essentially saying that any animal with any symptom, if wearing a Seresto collar, would have had the collar noted in the adverse signs reporting system. To connect the collar to the precise symptoms, however, is potentially not a realistic link. How many of those dogs (wearing Seresto collars) would have had the identical symptoms anyway; regardless of whether the collar was being worn at the same time, or not? This is a major issue with looking at raw data on adverse reactions without comparing it to a matched population not using that medication.

Let’s also put the precise numerical data to the test and interrogate the numbers. Since the EPA registration in 2012, over 25 million Seresto collars have been used by both dogs and cats in the USA; an enormous quantity of units. The incidence rate for all adverse events related to Seresto has however, been below 0.3%. Given the popularity of Seresto and its widespread and vast use, if you “do the math” of 0.3% x 25milion, there will of course be a number of animals reported. It would be pertinent to remember however, that these have occurred over a 9 year time period.

Additionally, reported effects are mostly mild – as the datasheet suggests.

Most of the reported side effects have pertained to non-serious effects such as skin site issues – hair loss, slight redness and itchiness. Neurological side effects (perhaps the most concerning – to me at least as a Veterinarian), are cited as “rare”. And as such, occur at an approximate incidence of less than 1 in 1,000 cases. The level of adverse effects does, therefore, not even approach the level of severity as suggested by the article.

Elanco also report in their response, that, “toxicologists and veterinarians have widely disputed the reports.”

Were these real or fake Seresto collars?

Another consideration, is whether many of the alleged side effects pertain to counterfeit products. In recent years, these have been produced and illegally sold to unknowing pet owners, and production of replica Seresto collars has been a growing problem for some time now. It was so severe that last autumn, Bayer (then the manufacturer) produced a video informing the general public of a number of ways in which to tell whether Seresto collars were counterfeit. Potentially many of the serious side effects reported, may actually therefore, not even relate to the legitimate form of the Seresto collar. 

Vetster option 02 (Blog)

Fraudulent products remain an ongoing concern. As such, it is always advised to purchase your Seresto collar, directly from a Veterinary Surgery rather than online or through any other means.

And moving forwards?

At the time of writing, the safety and efficacy of Seresto has been thoroughly supported. This is both from the scientific evaluation and data obtained from the product’s original registration and additionally, also through the current manufacturer’s own monitoring and surveillance reporting audit service. As such, no market recall or indeed any further action, has been suggested, neither required to be implemented.

Elanco continue to stand strong behind Seresto’s safety profile. The product remains available globally and as mentioned previously within this article, provides useful armoury in the fight against fleas and ticks and the latter’s role in vector borne disease.

So do vets still recommend its use? Right now, yes, if it’s suitable for the dog or cat in question.

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